The present invention relates to a catalyst for producing phthalic anhydride, and more particularly to a catalyst for producing phthalic anhydride by vapor phase catalytic oxidation of orthoxylene and/or naphthalane with molecular oxygen or gas containing molecular oxygen.
Catalysts for producing phthalic anhydride having a catalytic active substance mainly composed of vanadium oxide and titanium oxide supported on an inert carrier are widely known, and are disclosed, for example, in the Japanese Patent Publications 47-15323, 49-41036, 52-4538, and the Japanese Laid-open Patents 47-5661, 49-89694. These catalysts have their own features, and some of them are used industrially and achieving due results.
There is, however, an ample room for improvement of the catalyst performance, and regarding the selectivity to begin with, an increase of yield by only one percent is notable in its economical effect considering the scale of the producing equipment. Furthermore, improvement of selectivity makes it easier to operate for heat treatment and distillation until the products are obtained, and with the improvement of selectivity it is simultaneously expected to have an effect of producing products of high quality at low cost. Such improvement of selectivity is also important for using the raw materials effectively.
What is also important is the improvement of productivity and the maintenance of stable production by retaining the catalyst activity. One of the methods for enhancing the productivity is to perform oxidation reaction in high load reaction conditions by, for example, raising the material gas concentration. However, the reaction of obtaining phthalic anhydride from orthoxylene or naphthalene is accompanied by a violent heat generation, and the temperature rise in the hot spot area in high concentration condition is extreme, and an excessive oxidation reaction is produced, and the yield of the phthalic anhydride is lowered, while deterioration of the catalyst is extremely promoted.
Catalysts capable of withstanding such high load reaction conditions have been already proposed, for example, by the present applicant in the Japanese Patent Publication 59-1378.